With development and population of the RFID (Radio Frequency Identification) technique, RFID, served as a basis for a fast, real-time and accurate information acquisition and processing in high tech and standardization of messages, has been known across the world as one of top ten most significant techniques in this century. Because of gradual maturity of the standardization of the UHF frequency band in China, and requirements in applications such as logistics, smart transport and digital tourism, demands for track management of metal and non-metal assets in various fields have become increasingly clear, such as ultra-thin, ultra-small and ultra-light tag design, which put forward higher requirements for design of tag antennas.
With the development of the tag antenna technique, a micro-strip antenna with the following advantages has been presented: it has a low profile, a light weight and a low cost; it is able to be conformal with various carriers; it is suitable for mass production with printed circuit board technology; and it is easy to implement circular polarization, dual-polarization and dual-band operation, and so on; however, geometric shapes of conventional tag antennas are designed based on Euclidean geometry, and thus the minimum size that conventional tag antennas may be achieved remains limited.